Electric potential measuring device and image forming apparatus

ABSTRACT

An electric potential measuring device comprises a detection electrode of a conductive material disposed in opposition to an object and a movable structure comprised of a first solid material portion of another dielectric and a second solid material portion of another dielectric or a conductive material. A charge induced on the detection electrode by electric lines of force from the object is modulated by moving the movable structure with a drive mechanism, to measure an electric potential of the object. An image forming apparatus comprises the electric potential measuring device and an image forming means for performing a control of an image formation by using the electric potential measuring device.

TECHNICAL FIELD

The present invention relates to an image forming apparatus having anelectric potential measuring device applicable to the non-contact typepotential measuring device, a copier, a printer and the like.

BACKGROUND ART

Heretofore, for example, in an image forming apparatus having aphotosensitive drum and performing an image formation by anelectrophotography system, it is necessary to properly charge, that is,typically uniformly charge a potential of the photosensitive drum underany circumstance in order to constantly obtain a stabilized imagequality. Hence, the charged potential of the photosensitive drum ismeasured by using an electric potential measuring device (hereinafter,also referred to as “potential sensor”), and by utilizing themeasurement result, a feed back control is performed so as to uniformlykeep the potential of the photosensitive drum.

As for a conventional potential sensor, there is available a non-contacttype potential sensor. Here, a system called as a mechanically modulatedalternating electric field induction type is often used. According tothis system, the potential of the surface of a measuring object is afunction of the magnitude of the current taken out from a detectionelectrode contained in the potential sensor, given by the followingformula:

Here, Q denotes a charge to appear on the detection electrode, C acoupling capacitance between the detection electrode and the measuringobject, and V an electric potential of the surface of the measuringobject, and this capacity C is given by the following formula:

Here, A denotes a proportionality constant, S a detection electrodearea, and x a distance between the detection electrode and the measuringobject.

Although a potential V of the surface of the measuring object ismeasured by using these relationships, in order to accurately measurethe charge Q to appear on the detection electrode, it has been so farunderstood that the magnitude of the capacitance C between the detectionelectrode and the measuring object is better to be periodicallymodulated. As for the modulating method of this capacitance C, there areavailable two types of the method: a vibration capacitance type in whicha distance x between the detection electrode and the measuring object ischanged, and a chopper type in which an effective detection electrodearea S is changed. As for the chopper type, the following method isknown.

A first method is to effectively modulate the area S of the detectionelectrode. A fork-shaped metal shutter is inserted between the measuringobject and the detection electrode, and the shutter is periodicallymoved in a parallel direction with the surface of the measuring object,so that a shielding extent of the electric lines of force from themeasuring object reaching on the detection electrode is changed and thearea of the detection electrode is effectively changed, therebyrealizing the modulation of an electrostatic capacitance C between themeasuring object and the detection electrode (see U.S. Pat. No.4,720,682).

The second method is to dispose a metal shield member having an aperturein a position opposite to the measuring object and provide the detectionelectrode in a top end of the fork-shaped vibration element so that theposition of the detection electrode is changed in parallel directlybelow the aperture, thereby modulating the number of electric lines offorce reaching the detection electrode and modulating the electrostaticcapacitance C (see U.S. Pat. No. 3,852,667).

On the other hand, in order to downsize the electrophotographic imageforming apparatus, it is necessary to effect reduction in the diameterof the photosensitive drum and increase in the packaging density ofparts neighboring the drum, and at the same time, downsizings as well asa thin down of the potential sensor are required. However, in theabove-described sensor of the current mechanically modulated alternatingelectric field induction type, the inner volume of a sensor structure isoccupied by assembling parts such as a drive mechanism and the like forvibrating the fork-shaped shutter or the fork-shaped vibration element.Hence, for the downsizing of the potential sensor, it is essential todownsize these drive mechanisms.

In recent year, experiments have been reported in which by utilizing asemiconductor processing technology called as Micro Electro MechanicalSystem (MEMS), a fine mechanical structure is formed on a semiconductorsubstrate. The mechanically modulated alternating electric fieldinduction type potential sensor using such technology has been alsoreported. As a typical example, there is a case in which a shutterstructure having the fine opening portion prepared by the semiconductorprocessing technology is vibrated directly above the detectionelectrode, thereby attempting to measure the electric potential of themeasuring object (see U.S. Pat. No. 6,177,800).

Problems to be Solved by the Invention

In the potential sensor of the mechanically modulated alternatingelectric field induction type using the above-described conventionaltechnology, the fork-shaped shutter or the fork-shaped vibration elementin the top end of which is provided the detection electrode is vibrateddirectly above the detection electrode by using a piezoelectric elementdrive mechanism and the like so as to perform the modulation of thenumber of electric lines of force reaching the detection electrode. Inorder to effectively obtain a signal output of a practical level fromthe detection electrode, a typical area size of the detection electrodeis made about 2 mm×2 mm to be used, and a typical length of the shutteris made about 20 mm to be used. Consequently, as for a potential sensorto be mounted on a downsized electrophotographic image formingapparatus, further downsizing and thin down are required.

According to the MEMS technology, a movable mechanical part can beconstituted by a member having a thickness of about 1 μm to 100 μm.However, even if an attempt is made to prepare the shutter with anopening portion for the potential sensor by using such parts, its shapereceives restrictions from the viewpoint of a manufacturing processdifficulty and a mechanical strength.

The potential sensor used in the electrophotographic image formingapparatus is sometimes adversely affected in the sensor operation by afine particle such as an extra toner and the like generated in thevicinity of the photosensitive drum. Particularly, in the potentialsensor of a shutter structure having an opening, if the interval betweenthe detection electrode and the shutter is from several μm to hundredsμm, the fine particle such as the toner and the like infiltrates intothe space between the detection electrode and the shutter, and is apt toadversely affect the sensor operation. To enhance reliability of thesensor, a structure having no such opening is preferable.

Further, in the conventional potential sensor, the measurable area ofthe measuring object is approximately the same as the area of thedetection electrode, and it is difficult to measure a distribution ofpotential of the measuring object having the area larger than thedetection electrode.

In view of the above-described problems, the object of the presentinvention is to provide an electric potential measuring device and animage forming apparatus which are excellent in realizing a downsizing, ahigh performance, an advanced and sophisticated features, and a highreliability, and easily able to constitute a structure difficult to beaffected by contamination such as a fine particle and measure theelectric potential of an object to be measured as the measuring object.

DISCLOSURE OF THE INVENTION

According to an aspect of the present invention, there is provided anelectric potential measuring device comprises: a detection electrodecomprised of a conductive material and disposed in opposition to anobject to be measured; a movable structure comprised of a first solidmaterial portion comprised of a dielectric and a second solid materialportion comprised of a material having a relative dielectric constantdifferent from the dielectric or a conductive material and disposed soas to come to the object to be measured side of the detection electrode;and a drive mechanism for moving the movable structure in such a way asto change a positional relationship of the first and second solidmaterial portions for the detection electrode in an area between thedetection electrode and the object to be measured, wherein a chargeinduced on the detection electrode by electric lines of force emanatingfrom the object to be measured is modulated by moving the movablestructure by the drive mechanism, to measure an electric potential ofthe object to be measured. In such constitution, the shape of thestructure hardly receives restrictions, and it is possible to adopt asimple shape. Hence, the effecting of a downsizing, a high performanceand advanced and sophisticated features of the potential sensor can beeasily dealt with, and furthermore, the device can be made into astructure difficult to be affected by contamination and a fine particle.The movable structure is preferably a sheet-shaped structure.

In the electric potential measuring device of the above-describedinvention, the detection electrode is preferably formed on a substratedisposed in opposition to the object to be measured, and the movablestructure is periodically movable in a surface parallel to the substratejust above the surface of the object to be measured side of thedetection electrode. In this shape, a publicly known mechanism can beused as a drive mechanism of the structure, and further, the signalgenerated by a signal detection electrode can be processed withoutimposing a large load on a signal processing circuit.

In the electric potential measuring device of the above-describedinvention, the second solid material portion is preferably shapedperiodically in a predetermined direction, and an insulator layer isformed on the detection electrode, and an electric conductor layer of ashape having the same direction and the same periodic length as thesecond solid material portion is formed on the insulator layer (see FIG.1). Although a mutual disposition of the first solid material portionand the second solid material portion of the structure can beappropriately designed in conformity to use application, in this shape,a dynamic range can be made larger, and the potential sensor excellentin sensitivity, performance and reliability can be easily realized.

In the electric potential measuring device of the above-describedinvention, the second solid material portion is preferably shapedperiodically in a predetermined direction, and an electric conductorlayer of a shape having the same direction and the same periodic lengthas the second solid material portion is formed on the detectionelectrode through an insulator layer, and no insulator layer exists in apart in which the electric conductor layer is not formed but thedetection electrode is exposed (see FIG. 11). Even in such structure,the potential sensor being excellent in sensitivity, performance andreliability can be easily realized.

In the electric potential measuring device of the above-describedinvention, the second solid material portion is preferably shapedperiodically in a predetermined direction, and the detection electrodeis formed in a shape having the same direction and the same periodiclength as the second solid material portion. The electric conductorlayer of a shape having the same direction and the same periodic lengthas the second solid material portion is preferably formed on a portionin which the detection electrode is not formed through an insulatorlayer. (see FIG. 12). The shape of the detection electrode preferablyhas a divided structure, and is preferably constituted such that asignal generated by each of the divided detection electrode can beindependently measured and processed (see FIGS. 17A, 17B and 17C). Ifthis shape is used, it is possible to measure the distribution of thepotential of a larger area (for example, a length of a longer directionof A4 is about 30 cm). Further, after having discriminated a detectedelectric potential strength, by adding and amplifying the signals of aplurality of detection electrodes adjacent to one another, it ispossible to broaden the range of a measurable potential level. As forthe signal detection electrode of the divided structure, a shape formedin a shape simpler than the second solid material portion is alsopossible (see FIG. 19).

In view of the performance, the second solid material portion ispreferably comprised of the conductive material, and the conductivematerial is preferably grounded so that the electric lines of force areshielded by the second solid material portion.

According to another aspect of the present invention, there is providedan image forming apparatus which comprises the above electric potentialmeasuring device and an image forming means for performing a control ofan image formation by using the electric potential measuring device. Theimage forming means has, for example, a copy function, a printingfunction or a facsimile function. The present image forming apparatushas the image forming means to carry a photosensitive drum, and can takea shape to measure a charge potential on the photosensitive drum byusing the electric potential measuring device. This will be specificallydescribed by using FIG. 21. FIG. 21 is a schematic illustration of theperiphery of the photosensitive drum of an electrophotographicdeveloping apparatus using the potential sensor according to the presentinvention. In the periphery of a photosensitive drum 708, there areinstalled an electrostatic charger 702, an electric potential sensor701, an exposing machine 705, and a toner feeder 706. The surface of thedrum 708 is charged by the electrostatic charger 702, and the surface ofthe photosensitive drum 708 is exposed by the exposing machine 705, sothat a latent image is obtained. The latent image is adhered with thetoner by the toner feeder 706 so that a toner image is obtained.Further, the toner image is transferred on a transferred object 709 heldbetween a transferred object feed roller 707 and the photosensitive drum708, and the toner on the transferred object is adhered. By goingthrough these steps, the image formation is achieved. The charged stateof the drum 708 is measured by the potential sensor 701, and the signalis processed by a signal processor 703. A high voltage transformer 704is applied with a feedback to control the electrostatic charger 702 sothat a steady drum charge is realized, and a steady image formation isrealized.

According to a further aspect of the present invention, there isprovided an electric potential measuring method comprising the steps of:preparing a detection electrode comprised of a conductive material anddisposed in opposition to an object to be measured; a movable structurecomprised of a first solid material portion comprised of a dielectricand a second solid material portion comprised of a material having arelative dielectric constant different from the dielectric or aconductive material and disposed so as to come to the object to bemeasured side of the detection electrode; and moving the movablestructure in such a way as to change a positional relationship of thefirst and second solid material portions for the detection electrode inan area between the detection electrode and the object to be measured,whereby a charge induced on the detection electrode by electric lines offorce emanating from the object to be measured is modulated, to measurean electric potential of the object to be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a positional relationship between anobject to be measured and a substrate assembly and the movable structurecomprising an electric potential sensor in a first embodiment of thepresent invention;

FIG. 2 is a sectional view showing the positional relationship betweeneach component part and the object to be measured when the structure ismoved from the position of FIG. 1 in the first embodiment;.

FIG. 3 is a view showing that a numerical analysis of a potentialdistribution state in the vicinity of a substrate assembly and astructure shown in FIG. 1 is performed when a voltage is applied to theobject to be measured;

FIG. 4 is a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thestructure shown in FIG. 2 is performed when the voltage is applied tothe object to be measured;

FIG. 5 is a top view showing the structure and a mechanism for drivingthe structure in the first embodiment;

FIG. 6 is a top view showing an area provided on the substrate assemblyin order to install the driving mechanism of the structure in the firstembodiment;

FIG. 7 is a sectional view showing a second embodiment of the presentinvention;

FIG. 8 is a top view showing the structure in the second embodiment;

FIG. 9 is a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thestructure is performed when the voltage is applied to the object to bemeasured in the second embodiment;

FIG. 10 is a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thestructure is performed when the position of the structure is moved to aposition different from FIG. 9 in the event that the voltage is appliedto the object to be measured in the second embodiment;

FIG. 11 is a sectional view showing the structure of the substrateassembly in a third embodiment of the present invention;

FIG. 12 is a sectional view showing the structure of the substrateassembly in a fourth embodiment of the present invention;

FIG. 13 is a top view of a structure of the substrate assembly seen fromabove in the fourth embodiment of the present invention;

FIG. 14 is a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thedetection electrode of the structure is performed when the voltage isapplied to the object to be measured in the second embodiment of thepresent invention;

FIG. 15 a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thedetection electrode of the structure is performed when the voltage isapplied to the object to be measured in the third embodiment of thepresent invention;

FIG. 16 a view showing that the numerical analysis of the potentialdistribution state in the vicinity of the substrate assembly and thedetection electrode of the structure is performed when the voltage isapplied to the object to be measured in the fourth embodiment of thepresent invention;

FIG. 17A is a top view showing a constitution of the substrate assemblyin a fifth embodiment of the present invention;

FIGS. 17B and 17C are views showing sections cut in the lines 17B-17Band 17C-17C in FIG. 17A, respectively;

FIG. 18 is a view showing the positional relationship when the structureand the substrate assembly are installed in the vicinity of thephotosensitive drum of an electrophotographic device, in the fifthembodiment;

FIG. 19 is a sectional view showing a positional relationship betweenthe object to be measured and the substrate assembly as well as thestructure comprising the potential sensor in a six embodiment of thepresent invention;

FIG. 20 is a side view showing an example in case of having prepared thepotential sensor by using the ordinary assembling step in theembodiments of the present invention; and

FIG. 21 is a view representing the vicinity of the photosensitive drumof the electrophotographic developing apparatus using the potentialsensor according to the present invention.

According to the present invention, the movable structure, which ispreferably a sheet-shaped one (hwereinafter referred to as a“sheet-shaped structure”), comprised of the first solid material portioncomprised of a dielectric and the second solid material portioncomprised of a material having a relative dielectric constant differentfrom the first solid material portion or a conductive material is movedbetween an electrode detecting a signal and the object to be measured,thereby modulating a charge induced on the detection electrode byelectric lines of force from the object to be measured and measuring thepotential of the object to be measured. As a result, with anyrestriction scarcely received on the shape of the sheet-shapedstructure, it is easy to effect a downsizing, a high performance andadvanced and sophisticated features of the potential measuring device,and the potential measuring device of a structure difficult to beaffected by contamination such as a fine particle can be realized.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings. Throughout the drawings, the samereference numerals are attached to equivalent portions.

FIRST EMBODIMENT

A first embodiment of the present invention will be described based onFIGS. 1 to 6. FIG. 1 shows a whole structure of an electric potentialsensor according to the present embodiment. In FIG. 1, a detectionelectrode 101 and an insulator layer 102 are formed on a planarsubstrate 100, and an electric conductor layer 103 periodically disposedin a predetermined direction (here, the left and right directions of thedrawing) is disposed on the surface of the insulator layer 102(hereinafter, a portion comprised of the detection electrode, theinsulator layer and the electric conductor layer is referred to as“substrate assembly”). In the vicinity of this substrate assembly, asheet-shaped structure, in which a second solid material portion 110comprised of a conductive material is disposed in a striped shape (seeFIG. 5) in the same direction and the same cycle length as the periodicdisposition of the electric conductor layer 103 and a first slidmaterial portion 111 comprised of dielectric material is disposedbetween the second solid material portions 110, is disposed so as not tophysically contact the substrate assembly. The sheet-shaped structure isdisposed so as to come between the substrate assembly and an object tobe measured 120 when the substrate assembly is disposed in opposition tothe object to be measured 120. The sheet-shaped structure is movable tothe predetermined direction in parallel with the planer substrateassembly as a whole by a drive mechanism 112.

The detection electrode 101 is electrically connected to a signaldetection circuit 105 by a wiring 104. Each electric conductor layer 103and each second solid material portion 110 are grounded.

FIG. 1 shows a state in which the position of each second solid materialportion 110 of the sheet-shaped structure and the position of eachelectric conductor layer 103 inside the substrate assembly are in analmost aligned state for the object to be measured 120. In contrast tothis, in FIG. 2, the sheet-shaped structure is in a state of having beenmoved by half a distance of the period length of the disposition of thesecond solid material portion 110 from a state of FIG. 1 by operatingthe drive mechanism 112. Consequently, the position of each second solidmaterial portion 110 and the position of each portion of the detectionelectrode 101 in which the electric conductor layer 103 is not formedare in an almost aligned state for the object to be measured 120.

The operation of the potential sensor constituted as above will bedescribed. When a voltage is applied to the object to be measured 120,the electric lines of force emanating from the object to be measured 120are shielded by the second solid material portion 110, but reaches thedetection electrode 101 located between the electric conductor layers103 through the first solid material portion 111, thereby generating acharge here. At this time, the case where a relative position betweenthe sheet-shaped structure and the substrate assembly is in therelationship as shown in FIG. 1 and the case where the relative positionis in the relationship as shown in FIG. 2 are different in a volume ofelectric field in which the detection electrode 101 is exposed, and inthe charge induced on the detection electrode 101, accordingly. Thecharging and discharging of this induced charge is turned into acurrent, a voltage and the like, and is measured by a signal detectioncircuit 105. As for the method for detecting the voltage, there isavailable a passive method in which the measurement is made by using avoltage drop by a known resistor. Further, there is available an activezero method for adjusting the potential of the electric conductor layer103 and the like so as to make a charging and discharging currentgenerated in the detection electrode zero, by using a potentialadjusting element circuit, thereby measuring the potential of the objectto be measured. In case of using this active zero method, the electricconductor layer 103 and the like are not grounded to earth, butconnected to the potential adjusting element circuit.

FIGS. 3 and 4 represent the result of a numerical analysis of a state inwhich the electric lines of force reach the detection electrode throughthe first solid material portion 111 of a sheet-shaped structure,respectively, when a voltage is applied to the object to be measured 120in the state of FIGS. 1 and 2. The numerical analysis is performed byusing a simplified analyzing model.

In FIGS. 3 and 4, the sheet-shaped structure having a thickness of 10 μmis installed 3 mm downward from the object to be measured 120. Thesheet-shaped structure is comprised of a first solid material portion111 comprised of a dielectric and a conductive material, and iscomprised of a second solid material portion 110 electrically grounded,and these are alternately disposed in a period of 40 μm. Further, thedetection electrode 101 in the analyzing model is installed 5 μmdownward from the first solid material portion 111.

In FIG. 3 corresponding to the state of FIG. 1, the voltage of 800 V isapplied to the object to be measured 120, and the electric lines offorce radiated from the object to be measured reach the detectionelectrode 302 through the first solid material portion 111. At thistime, contour plot of equipotential lines joining the points having theequal potential in the space between the object to be measured 120 andthe detection electrode 101 is represented by black and white shadingspattern as shown by 301 in FIG. 3. However, in FIG. 3, a state only inwhich the potential changes from 0 V to 2 V in the space in the vicinityof the sheet-shaped structure and the detection electrode isrepresented.

Even if the sheet-shaped structure having no region such as a physical“hole” is inserted between the object to be measured 120 and thedetection electrode 101 from FIG. 3, it is understood that the electriclines of force reach the detection electrode through the dielectric onthe condition that a part of the sheet-shaped structure is comprised ofa dielectric. Furthermore, it is also understood that the location ofthe electric lines of force passing through the sheet-shaped structurecan be controlled by constituting the sheet-shaped structure byappropriately combining the conductive portion 110 and the dielectricportion 111.

FIG. 4 represents the result of performing the numerical analysis on thestate of FIG. 2. Here, the sheet-shaped structure moves for thedetection electrode by a half of the length of the period length 40 μmof the disposition of the second solid material portion 110 and thefirst solid material portion 111, that is, by 20 μm in the right or theleft direction of the drawing, and as a result the detection electrode101 is located down below the second solid material portion 110. At thistime, contour plot of equipotential lines formed by the electric linesof force radiated from the object to be measured 120 are represented by401.

As evident from FIGS. 3 and 4, a change in a relative position betweenthe first solid material portion 111 comprised of the dielectric and thedetection electrode 101 changes the potential in the periphery of thedetection electrode 101, thereby changing the number of electric linesof force reaching a detection electrode 101 to change the charge inducedon the detection electrode 101.

Accordingly, as shown in FIGS. 1 and 2, if the sheet-shaped structurewherein the first solid material portion 111 and the second solidmaterial portion 110 are periodically disposed is inserted between theobject to be measured 120 and the detection electrode 101 and thesheet-shaped structure is periodically moved, the charge induced on thedetection electrode 101 can be modulated, and based on this, it ispossible to detect a surface potential of the object to be measured 120by signal detection circuit 105.

Here, the drive mechanism 112 of the potential sensor of the presentembodiment and the disposition of each component part will be describedby using the top views of FIGS. 5 and 6. As shown in FIG. 5, both endsof a vibration direction of the sheet-shaped structure are connected toa piezoelectric element 501 in which electrodes 502 and 503 are formed,and a piezoelectric element 504 in which electrodes 505 and 506 areformed. A synchronous alternating current voltage is applied to a groupof electrodes 502 and 503 and a group of electrodes 505 and 506 throughwirings 508 and 509 from a piezoelectric element-driving power source507 so as to vibrate both of the piezoelectric elements. As a result,the position of the sheet-shaped structure is moved.

Further, in FIG. 5, the second solid material portion 110 is grounded byan earth wiring 511 and an electric wiring 512. In this way, theelectric lines of force are satisfactorily shielded in the second solidmaterial portion 110.

FIG. 6 shows a substrate assembly for disposing the sheet-shapedstructure and the piezoelectric elements 501 and 504 shown in FIG. 5.The detection electrode 101, insulator layer 102 and electric conductorlayer 103 are disposed in a substrate 100. Further, the electricconductor layer 103 is grounded by electric wirings 601 and 602 so thatthe shielding of the electric lines of force coming here issatisfactorily performed to control a noise component of the potentialsensor. The detection electrode 101 is connected to the signal detectioncircuit 105 by a signal wiring 104. Space regions 603 and 604 forinstalling the piezoelectric elements 501 and 504 are secured on thesubstrate 100, and these piezoelectric elements are mounted on thesespace regions. At this time, it is easy to dispose the sheet-shapedstructure in such a way not to contact a substrate assembly byappropriately executing a method for connecting the piezoelectricelements 501 and 504 to the sheet-shaped structure.

As for the drive mechanism of the sheet-shaped structure, the otherpublicly known drive mechanism utilizing a static electricity, amagnetic field, heat, an electromagnetic force may be used.

SECOND EMBODIMENT

Next, a second embodiment of the potential sensor of the presentinvention will be described by using FIGS. 7 to 10. FIG. 7 represents asectional schematic illustration of the present embodiment in which thestructure of a sheet-shaped structure is different comparing to thefirst embodiment. In the present embodiment, a second solid materialportion 110 comprised of a thin film conductive material on a firstsolid material portion 111 which is comprised of one sheet of asheet-shaped dielectric is periodically disposed in a striped shape (seeFIG. 8) in a predetermined direction. This structure is easy to prepare.The other constitutions are the same as the first embodiment.

FIG. 8 represents a top view of the sheet-shaped structure shown in FIG.7. The second solid material portion 110 is disposed in a striped shape,and is electrically grounded through wirings 511 and 512. Thesheet-shaped structure can periodically move in the predetermineddirection on a substrate assembly by a drive mechanism 112 connected toa first solid material portion 111.

FIGS. 9 and 10 represent an analyzing model and a calculation result incase of numerically analyzing the present embodiment shown in FIG. 7. Afirst solid material portion 111 having a thickness of 10 μm is disposed3 mm downward from an object to be measured 120, and the second solidmaterial portion 110 having a thickness of 1 μm and a width of 20 μm isdisposed in a period of 40 μm above the first solid material portion111. Further, the detection electrode 101 in the analyzing model isdisposed 5 μm below from the first solid material portion.

In FIG. 9, a voltage of 800 V is applied to the object to be measured120, and electric lines of force radiated from the object to be measuredreach the detection electrode 101 through the first solid materialportion 111. In this case, contour plot of equipotential lines of thespace between the object to be measured 120 and the detection electrode101 are represented by black and white shadings. They are shown byshapes as shown by 902 of FIG. 9. In FIG. 9 similarly as FIG. 3, a stateonly in which the potential changes from 0 V to 2 V in the space in thevicinity of the sheet-shaped structure and the detection electrode 101is represented due to a limit of the drawing. As evident from FIG. 9,even in the constitution in which the sheet-shaped structure iscomprised of the second solid material portion 110 periodically disposedon the first solid material portion 111 and its surface, the electriclines of force radiated from the object to be measured 120 are shieldedin a part in which the second solid material portion 110 exists.However, in a part in which the second solid material portion does notexist but the first solid material portion 111 only exists, it ispossible for the electric lines of force to reach the detectionelectrode 101 through the first solid material portion.

FIG. 10 represents a distribution of the potential in a state in whichthe sheet-shaped structure is moved from the state in FIG. 9 to theright or the left direction of the drawing for the detection electrode101 by 20 μm, that is, by half a distance of the disposition period ofthe second solid material portion 110. A potential distribution 1001above the detection electrode 101 is evidently different from apotential distribution 902 of FIG. 9, and from this, it is understoodthat a charge induced by an electric field from the object to bemeasured 120 and appeared on the detection electrode 101 is differentbetween the states of FIGS. 9 and 10.

Consequently, it is understood that the sheet-shaped structure shown inFIGS. 7 and 8 also enables the charge induced on the detection electrode101 to be modulated by periodically moving the sheet-shaped structure.

THIRD EMBODIMENT

Next, a third embodiment of the potential sensor of the presentinvention will be described with reference to FIG. 11. In the thirdembodiment, the structure of a substrate assembly is different,comparing to the first and the second embodiments. An insulator layer102 has the same periodic structure as an electric conductor layer 103periodically disposed and is disposed directly below the layer 103. Adetection electrode 101 formed on a substrate 100 is periodicallyexposed in the space of an object to be measured side through aclearance gap of the insulator layers 102. This constitution alsoenables a charge induced on the detection electrode 101 to be modulated,and similarly as the above-described embodiment, the potential of theobject to be measured to be measured.

FOURTH EMBODIMENT

A fourth embodiment of the potential sensor of the present inventionwill be described with reference to FIGS. 12 and 13. In a substrateassembly of FIG. 12, one insulator layer 102 is formed on a substrate100, and an electric conductor layer 103 is periodically disposed on thelayer 102. Between the electric conductor layers 103, the detectionelectrode 101 is formed directly on the substrate 100, and there existsno insulator layer 102. That is, the detection electrodes 101 areseparated from each other by the insulator layer 102, and do not existjust under the insulator layer 102. Further, there exists neitherinsulator layer 102 nor the electric conductor layer 103 on thedetection electrode 101, and the detection electrodes are periodicallyexposed in the space of the object to be measured side through intervalsof the insulator layers 102.

FIG. 13 is a view observing FIG. 12 from above. The rectangulardetection electrodes 101 are disposed on the substrate in a plurality ofwindow portions provided in the insulator layer 102 on the substrate100, and are shaped so as to be exposed in the space of the object to bemeasured side, and further, shielded at both sides thereof by theelectric conductor layers 103 which are grounded. In this way, similarlyas the above-described embodiment, the electric lines of force from theobject to be measured reach the detection electrode 101 almost directlyfrom the front side only, and it is, therefore, possible to control anoise component and measure an accurate potential.

In this structure, the signals generated at each detection electrode 101by the periodic movement of the sheet-shaped structure are transmittedto the signal detection circuit 105 through the wirings 106, 108 and 104held between the insulator layer 102 and the substrate 100.

FIGS. 14, 15 and 16 show a result of numerical analysis of thedistribution in the vicinity of the detection electrode of the electricfield emanating from the object to be measured when three types of thesubstrate assembly as described in the second, third and fourthembodiments are used together with the sheet-shaped structure in thesecond embodiment. In this analysis, a voltage of 800 V is applied tothe object to be measured, and the first solid material portions 111having a thickness of 10 μm are disposed 3 mm downward from the objectto be measured, and the second solid material portions 110 having athickness of 1 μm and a width of 20 μm are disposed on the first solidmaterial portion 111 in a periodic pattern of 40 μm. Each substrateassembly is disposed 5 μm below from this sheet-shaped structure.Equipotential distributions 1401, 1501 and 1601 are represented by blackand white shadings in the rage of 0 V to 0.1 V due to a limit of thedrawings.

From FIGS. 14, 15 and 16, it is easily understood that, in any one ofthree types of the substrate assembly structure used in the second,third and fourth embodiments, respectively, the electric potentialdistribution is generated in the vicinity of the detection electrode101, and each is a structure usable as a potential detection electrodeof the potential sensor.

Further, it is understood that the case where the insulator layer 102 isavailable on an exposed detection electrode (second embodiment, FIG. 14)and the case where the layer is not available (the third embodiment,FIG. 15, the fourth embodiment, FIG. 16) are different in potentialdistribution of the surface of the detection electrode 101. Hence, it ispossible to change the disposition of the electric conductor layer, theinsulator layer and the detection electrode so as to be able to obtainan optimum potential distribution according to a use application and adesign of the substrate assembly.

FIFTH EMBODIMENT

Next, a fifth embodiment of the present invention will be described withreference to FIGS. 17A, 17B and 17C. FIG. 17A is a top view of asubstrate assembly structure in the fifth embodiment. FIGS. 17B and 17Care views showing sections cut in the lines 17B-17B and 17C-17C in FIG.17A. A rectangular detection electrode 101 is disposed in plurality on asubstrate 100, and is shaped so as to be exposed through a plurality ofwindow portions provided in an insulator layer 102, and further,surrounded in the periphery by a grounded electric conductor layer 103.The signal generated by each divided detection electrode 101 isconnected to a signal detection calculation circuit 105 by eachindependent wirings 104 and 106.

In a potential sensor of the present embodiment, it is possible toindependently detect an inductive electrostatic charge generated in eachof a plurality of rectangular detection electrodes 101 by allowing thesignal detection calculation circuit 105 to carry a function capable ofindependently processing a plurality of signals. That is, the signaldetection calculation circuit 105 has the function of receiving each ofsignals from a plurality of the electrodes, amplifying each of thereceived signals in the circuit, and calculating the results of theamplifications. Consequently, even in the case where a potentialdistribution of the object to be measured surface is not uniform, it ispossible to dispose a plurality of detection electrodes on the substrateassembly at a desired position and to measure a surface potential of thedesired position of the object to be measured.

In theory, since there is no restriction imposed on the size of thesubstrate assembly and the sheet-shaped structure, it is also possibleto measure the potential distribution of the desired region at desiredintervals by using an appropriate manufacturing method and material.

FIG. 18 shows a structural example in which the potential sensor of thefifth embodiment is installed in opposition to a photosensitive drum 708of an electrophotographic printing machine having the same length ofabout 290 mm as the longitudinal direction of a printing paper 1814 ofA4 size. By using an appropriate design, material and manufacturingmethod, the substrate assembly and a sheet-shaped structure areprepared, which are installed at a position opposite to thephotosensitive drum 708, thereby collectively measuring the potentialdistribution of the A4 longitudinal direction.

By summing signals induced in a plurality of detection electrodes 101adjacent to one another by the potential sensor of the fifth embodiment,an effect of allowing a detection sensitivity to substantially increasecan be obtained. As can be understood from formula (2), this summingfunction utilizes a fact that a signal output generated in the detectionelectrode is proportionate to an area of the detection electrode in thecase of a mechanically modulated alternating electric field inductiontype, and this function can be therefore applied in the case where,because of a low surface potential of the object to be measured, anelectrostatic charge induced in each detection electrode on thesubstrate assembly is small and is difficult to detect. This functioncan be realized by building into the signal detection calculationcircuitry 105 a function for deciding the relative intensity of eachsignal from the detection electrodes 101, a function for recombining thecircuits in such a way that the signals from a plurality of theelectrodes are summed when the signals are extremely small and at such alevel that it is difficult to detect them, and a function for amplifyingthose summed signals.

SIXTH EMBODIMENT

A sixth embodiment of the present invention will be described withreference to FIG. 19. In the embodiments described so far, the detectionelectrode 101 of the substrate assembly has zoned its electric fieldreception portion by insulator layer 102 or surrounded it by electricconductor layer 103, so that electric lines of force coming from anobject to be measured were received almost directly from the front sideof the detection electrode. However, a structure to simply periodicallydispose the detection electrode is also possible, and this structure isadopted in the sixth embodiment. As shown in FIG. 19, in the presentembodiment, a sheet-shaped structure uses that of the first embodiment,and a substrate assembly uses that on which a plurality of rectangulardetection electrodes 101 on a substrate 100 are disposed in the sameperiod as the disposition period of the first solid material portion 111and a second solid material portion 110 of the sheet-shaped structure.The detection electrode 101 is connected to a signal detection circuit105 by a wiring 104.

Although a potential measuring theory is substantially the same as theembodiments described so far, in the present embodiment, since thedetection electrode 101 is not zoned or surrounded by an insulator layerand an electric conductor layer, advancing extents of electric lines offorce into the detection electrode 101 are controlled only by thesheet-shaped structure. On the other hand, the constitution of thesubstrate assembly becomes simple.

As for the method for preparing a potential sensor according to thepresent invention, a micro-machine technology which forms a microstructure by using a semiconductor processing technology is arepresentative example. When this technology is used, it is possible tobatch-mold small type potential sensors on a silicon substrate in alarge quantity. Specifically, by using the semiconductor processingtechnology such as a dry-etching technology, a thin-film formationtechnology, a sacrifice layer etching technology and the like, asubstrate assembly structure, a sheet-shaped structure and a drivemechanism can be formed on the silicon substrate.

Of course, the method for preparing the potential sensor according tothe present invention is not restricted to such semiconductor processingtechnology. FIG. 20 shows a preferable example. In this example, asubstrate assembly 1900 is formed of a print circuit substrate usingglass epoxy, and a sheet-shaped structure 1901 is composed by forming anappropriately shaped metal thin film on a dielectric film such aspolyimide into a film. Drive parts 1902 and 1903 connected to a drivecircuit 1905 are mounted on the substrate assembly 1900 which isconnected to a signal detection circuit 105, and the sheet-shapedstructure 1901 is mounted between the drive parts 1902 and 1903 so asnot to contact the substrate assembly 1900. Such constitution can beprepared by using an electronic part assembling step.

INDUSTRIAL APPLICABILITY

The potential measuring device of the present invention may be appliedto a system comprised of a plurality of devices such as, for example, ahost computer, an interface device, a reader, a printer and the like,and may be applied to one device, for example, an apparatus comprised ofa copying machine and a facsimile.

1. An electric potential measuring device comprising: a signal detectionelectrode; a movable structure comprised of a first solid materialportion and a second solid material portion; and a drive mechanism formoving the movable structure in such a way as to change a positionalrelationship of the first and second solid material portions for thesignal detection electrode, wherein the first solid material portion iscomprised of a dielectric, the second solid material portion iscomprised of a conductive material, and a charge induced on the signaldetection electrode is modulated by moving the movable structure, tomeasure an electric potential of the object to be measured.
 2. Theelectric potential measuring device according to claim 1, wherein saiddetection electrode is formed on a substrate disposed in opposition tothe object to be measured, and said movable structure is periodicallymovable in a surface parallel to the substrate just above the surface ofthe object to be measured side of the detection electrode.
 3. Theelectric potential measuring device according to claim 1, wherein saidsecond solid material portion is periodically shaped in a predetermineddirection, and an insulator layer is formed on said detection electrode,and an electric conductor layer of a shape having the same direction andthe same periodic length as the second solid material portion is formedon the insulator layer.
 4. The electric potential measuring deviceaccording to claim 1, wherein said second solid material portion isperiodically shaped in a predetermined direction, and an electricconductor layer of a shape having the same direction and the sameperiodic length as the second solid material portion is formed on saiddetection electrode through an insulator layer, and no insulator layerexists in a part in which the electric conductor layer is not formed butthe detection electrode is exposed.
 5. The electric potential measuringdevice according to claim 1, wherein said second solid material portionis periodically shaped in a predetermined direction, and said detectionelectrode is formed in a shape having the same direction and the sameperiodic length as the second solid material portion.
 6. The electricpotential measuring device according to claim 5, wherein the electricconductor layer of a shape having the same direction and the sameperiodic length as the second solid material portion is formed on aportion in which the detection electrode is not formed through aninsulator layer.
 7. The electric potential measuring device according toclaim 6, wherein the shape of said detection electrode has a dividedstructure, and is constituted such that a signal generated by each ofthe divided detection electrode can be independently measured andprocessed.
 8. The electric potential measuring device according to claim1, wherein said second solid material portion is comprised of saidconductive material, and the conductive material is grounded.
 9. Theelectric potential measuring device according to claim 1, wherein saidmovable structure is a sheet-shaped structure.
 10. An image formingapparatus, comprising the electric potential measuring device accordingto claim 1 and an image forming means for performing a control of animage formation by using the electric potential measuring device.
 11. Anelectric potential measuring method comprising the steps of: preparing adetection electrode comprised of a conductive material and disposed inopposition to an object to be measured; a movable structure comprised ofa first solid material portion comprised of a dielectric and a secondsolid material portion comprised of a material having a relativedielectric constant different from the dielectric or a conductivematerial and disposed so as to come to the object to be measured side ofthe detection electrode; and moving the movable structure in such a wayas to change a positional relationship of the first and second solidmaterial portions for the detection electrode in an area between thedetection electrode and the object to be measured, whereby a chargeinduced on the detection electrode by electric lines of force emanatingfrom the object to be measured is modulated, to measure an electricpotential of the object to be measured.